As illustrated in FIG. 5 to FIG. 7, a roller bearing 21 includes: an outer member 23 having a cylindrical outer ring raceway 22 on its inner circumferential surface; an inner member 25 having a cylindrical inner ring raceway 24 on its outer circumferential surface; and a plurality of rollers 26 that are rollably provided between the outer ring raceway 22 and the inner ring raceway 24.
The rollers 26 are rollably held by a holder 27 the entirety of which is formed in a cylindrical shape. The holder 27 has pockets 28 that respectively house the rollers 26, at predetermined intervals in its circumferential direction. The holder 27 includes: pillar parts 29 between the pockets 28 adjacent to each other in the circumferential direction; and annular parts 30 on both sides in the axial direction of the pillar parts 29.
Inner protrusions 31 and outer protrusions 32 that prevent the rollers 26 from coming off are respectively provided on the inner diameter side and the outer diameter side of the pillar parts 29 of the holder 27.
Oil channels 33A and 33B that extend inward and outward in the radial direction are provided in, for example, three portions of a middle portion and both ends in the axial direction of each pillar part 29 so as not to overlap with portions in which the inner protrusions 31 and the outer protrusions 32 are formed. Then, lubricant oil is centrifugally circulated from the inside to the outside in the radial direction of the holder 27 through the oil channels 33A and 33B, whereby a flow of the lubricant oil and the amount of lubricant oil in the roller bearing 21 are secured.
The roller bearing 21 configured as described above is used for, for example, the case where a planetary gear (outer member 23) is pivotally supported by a support pin (inner member 25) in each reducing gear mechanism of a planetary gear reducer.
In such a case, the gap formed between the outer member 23 and the holder 27 defines an outer oil passage 34, the gap formed between the inner member 25 and the holder 27 defines an inner oil passage 35, and the lubricant oil in a housing that constitutes the outer shape of the planetary gear reducer passes through the outer oil passage 34 and the inner oil passage 35 to flow into each pocket 28 of the roller bearing 21. Then, the lubricant oil that has flown thereinto is circulated by centrifugal force generated by rotation of the planetary gear, from the inside to the outside in the radial direction of the holder 27 through the oil channels 33A and 33B. This enhances the lubricity of the roller bearing 21.
Meanwhile, in the case where the roller bearing 21 is used for such a planetary gear reducer as described above, dusts such as wear debris and seal pieces of a seal member are generated from mesh surfaces of gears during operation, and the dusts invade each pocket 28 of the roller bearing 21 along with the flow of the lubricant oil.
The inner protrusions 31 and the outer protrusions 32 that prevent the rollers 26 from coming off are provided to the pillar parts 29 that respectively partition the pockets 28 of the roller bearing 21.
Accordingly, if each roller 26 rotates in contact with the inner protrusions 31 and the outer protrusions 32 of each pillar part 29, the lubricant oil on the outer surface of the roller 26 is scraped by the inner protrusions 31 and the outer protrusions 32, and the dusts are accumulated in contact portions between: the roller 26; and the inner protrusions 31 and the outer protrusions 32.
As a result, there occurs a problem that the roller 26 in each pocket 28 rubs against the dusts, particularly metal wear debris such as iron powder accumulated in portions of the inner protrusions 31 and the outer protrusions 32, and thus is worn away in a short time.
Particularly in recent years, for example, gear reducer manufacturers tend to omit finish processing of gears along with demands for cost reduction, so that the surface roughness is increasing. As a result, rough protrusions come off due to mesh between the gears, and a large amount of wear debris is generated in many cases. Accordingly, preventing rollers from being worn by metal wear debris is becoming an important issue.
As a countermeasure against such wear debris, Patent Literature 1 and Patent Literature 2 describe that a groove 36 that captures foreign substances and wear debris is provided on a wall surface of each pillar part 29 between the pockets 28.